Generally, the conventional faucet with pipe-in-pipe structure (as shown in FIG. 16) comprises a faucet body (70), which has a water inlet chamber (71) and a water outlet chamber (72) respectively formed at a bottom portion and a top portion of the faucet body (70). A valve channel (73) formed at a lateral side of the faucet body (70) is configured to provide loading for a control valve (80). A central bottom portion of the valve channel (73) has two cold and hot water inlet tubes (74) and a filtered water inlet tube (75) to receive cold and hot water sources and a filtered water source respectively, and a tap water outlet hole (76) and a filtered water outlet hole (77) upwardly penetrate a bottom of the water outlet chamber (72) respectively. The water outlet chamber (72) has a water outlet tube (90), and the water outlet tube (90) further comprises an outer tube (91) and an inner tube (92) which is formed inside the outer tube (91). In actual application, the faucet can provide tap water by rotating a handle, which is connected to the control valve (80) of the faucet, in one direction. By rotating the handle with different angles, the faucet can provide cold water, hot water, or different mixing ratios of hot water and cold water which are pre-mixed in the ceramic control valve (80). Also, since the tap water outlet hole (76) is connected with the outer tube (91) of the water outlet tube (90), cold water, hot water or warm waters from different mixing ratios of cold water and hot water can flow out of the faucet through the outer tube (91). On the other hand, the faucet can provide the filtered water by rotating the handle in the other direction. The filtered water can flow from the filtered water inlet tube (75) through the valve channel (73) into the control valve (80), and flows from the filtered water outlet hole (77) of the control valve (80) through the inner tube (92) of the water outlet tube (90) out of the faucet.
However, the conventional faucet is disadvantageous because: (i) when the faucet body (70) of the conventional faucet is casted, it still needs to have a second manufacturing process for the cold and hot water inlet tubes (74), the filtered water inlet tube (75), the tap water outlet hole (76), and the filtered water outlet hole (77), resulting in increasing the difficulty and cost of production process; and (ii) the conventional faucet can only be used after the water inlet chamber (71), the water outlet chamber (72), the cold and hot water inlet tubes (74), the filtered water inlet tube (75), the tap water outlet hole (76) and the filtered water outlet hole (77) are settled inside the faucet body (70). As a result, it increases the complexity of channels inside the faucet body (70) and the difficulty of subsequent manufacturing process. Therefore, there remains a need for a new and improved design for a faucet with pipe-in-pipe structure to overcome the problems presented above.